Ohmic contact for nitride-based semiconductor device

1. A nitride-based semiconductor device comprising: a nitride-based semiconductor structure, the semiconductor structure comprising an AlGaN semiconductor; and an ohmic contact to the AlGaN semiconductor, the ohmic contact including: a contact layer comprising at least Aluminum (Al) and Indium (In) directly on the semiconductor structure; and a metal layer directly on the contact layer.

2. The semiconductor device of claim 1 , wherein the contact layer further comprises Gallium (Ga) and Nitrogen (N).

3. The semiconductor device of claim 1 , wherein a molar fraction of at least one of Al or In in the contact layer increases or decreases from a metal layer-contact layer interface toward a contact layer-semiconductor structure interface.

4. The semiconductor device of claim 1 , wherein a thickness of the contact layer is between approximately one nanometer and approximately five thousand nanometers.

5. The semiconductor device of claim 1 , wherein an Al composition of the contact layer is greater than approximately one percent.

6. The semiconductor device of claim 1 , wherein an In molar fraction of the contact layer exceeds approximately 0.001%.

7. The semiconductor device of claim 1 , wherein a metal layer-contact layer interface comprises a plurality of sharp pyramids protruding from the metal layer into the contact layer.

8. The semiconductor device of claim 1 , wherein the metal layer comprises: a plurality of needles contacting the contact layer; and an overlaying contact metal that connects each of the plurality of needles.

9. The semiconductor device of claim 1 , wherein the semiconductor device is configured to operate as one of: a light emitting diode, a laser, a bipolar junction transistor, a heterojunction bipolar transistor, a thyristor, and a photodiode.

10. The semiconductor device of claim 1 , wherein the semiconductor structure comprises a p-n junction.

11. The semiconductor device of claim 1 , wherein the AlGaN semiconductor comprises a high molar fraction of Al.

12. The semiconductor device of claim 1 , wherein the AlGaN semiconductor is a Mg-doped AlGaN semiconductor.

13. A nitride-based semiconductor device comprising: a nitride-based semiconductor structure, wherein the semiconductor structure comprises an AlGaN semiconductor; and an ohmic contact to the AlGaN semiconductor, the ohmic contact including: a contact layer comprising Aluminum (Al), Indium (In), Gallium (Ga), and Nitrogen (N) on the semiconductor structure; and a metal layer on the contact layer, wherein a molar fraction of one of Al or In in the contact layer increases or decreases from a metal layer-contact layer interface toward a contact layer-semiconductor structure interface, and wherein the metal layer-contact layer interface includes at least one of: a plurality of sharp protruding metal pyramids or a plurality of metal needles.

14. The semiconductor device of claim 13 , wherein the other of Al or In has a substantially constant molar fraction throughout the contact layer.

15. The semiconductor device of claim 13 , wherein the contact layer comprises a p-type semiconductor.

16. A nitride-based semiconductor device comprising: a nitride-based semiconductor structure; and an ohmic contact to an active layer in the semiconductor structure, the ohmic contact including: a contact layer comprising at least Aluminum (Al) and Indium (In) directly on the semiconductor structure; and a metal layer directly on the contact layer, wherein the metal layer protrudes into the contact layer, wherein the active layer comprises Mg-doped AlGaN.

17. The semiconductor device of claim 16 , wherein a molar fraction of one of Al or In in the contact layer increases or decreases from a metal layer-contact layer interface toward a contact layer-semiconductor structure interface.

18. The semiconductor device of claim 16 , wherein the contact layer further comprises Gallium (Ga) and Nitrogen (N).